INDIVIDUAL WILDERNESS WATER TREATMENT

 

By Dr. Bob Armstrong, N7XJ

Contributing editor, The ARS Sojourner

 

This is an outline of my lecture notes. The material is from Wilderness Medicine textbooks and journal articles, updated January 2008. It relates to backpacking in North America. It is based on my training as a microbiologist and chemist in college and my experience as a medical doctor.

 

WATER PURIFICATION AND DISINFECTION

 

Virtually all water is contaminated to some degree and treatment is always appropriate. Water might contain:

 

-Industrial chemicals and pesticides.

- Naturally occurring organic and inorganic toxins.

- Benign ground and water organisms.

- Disease-causing microbes from animal and human waste.

 

Removal of chemical hazard is called "purification". Chemicals cause about 30% of water borne gastroenteritis (primarily diarrhea). Little is written about individual water purification in the wilderness. Filters and Activated Charcoal are the primary tools (see below).

 

Destruction of disease-causing microbes is called "disinfection". Infected water is known to have caused outbreaks of illness along popular trails and waterways.

 

WATER AND INFECTIOUS DISEASE

 

With a few exceptions, infected water causes diarrhea. Infected water may account for as much as 15% of wilderness acquired diarrheal disease.

 

Most infectious diarrhea is spread via the "oral-fecal" route, which is the spread of disease from human or animal waste by unwashed hands. Would you care to share some trail mix?

 

It makes little sense to fuss about infected water if you fail to wash your hands. Field Sanitation is an important topic not otherwise addressed here.

 

TYPES OF WATER-BORNE GERMS:

 

Disease can be caused by a variety of microorganisms which differ in size and characteristics:

 

-Bacteria: The most common are "coliforms" found in stool, including enterotoxic E. Coli, Salmonella, and Shigella. Bacteria are moderately small and fairly common.

 

-Virus: Hundreds of kinds of virus have been shown to cause diarrhea, including the notorious Norwalk virus and Rotavirus. Serious non-diarrheal viral diseases that can be spread by water include hepatitis A and E and polio. Virus are very small and are by far the most common cause of water-bourne diarrhea.  They are usually too small to be filtered from water and are best inactivated by chlorine or other "killing".

 

-Protozoa: Giardia and Crytosporidium are common protozoal diseases that can cause serious diarrhea. Protozoa are moderately large and quite common.  They are not easily killed by chemicals such as chlorine, and are best removed by filtration.

 

-Parasites: Usually come from soil and don’t cause diarrhea. Ascaris (and some other "worms") and Echinococcus are examples of some parasites that can be spread by water. Parasites and their eggs are fairly large and relatively uncommon in North American waters.

 

Disease can come from drinking or taking in very small amounts of infected water when swimming, during white-water adventures, or fishing. Bacteria from water can multiply to significant numbers in food.

 

RECOGNIZING SAFE WATER

 

We prefer clear, cold, running water that tastes and smells good, but the appearance of water can be deceiving.

 

The best predictor of safe water is the amount of human and animal activity in the area. Infectious disease mostly comes from waste from people and domestic animals, such as dogs, cattle, horses and other pack animals.

 

-Taste and smell are caused by small amounts of chemical that are usually not harmful.

 

- Running water is not always safer: Running water loses, but also picks up contaminants continually. Rain can "flush out" streams or can wash contaminants in. Look for evidence that human or animal waste could have been washed into the water.

 

- Standing water is not necessarily bad. It might contain more organic material ("pond scum") that traps microbes, but contaminants settle out of still water more easily. Avoid stirring up sediment whenever you gather water.

 

- Cold water might be more dangerous than warm: Heat and sunlight kill germs, so warm or tepid water near the surface is generally safer than cold water at the bottom. Microorganisms survive much longer in cold water than warm, and can live for weeks or months in ice.

 

- Clear water: Clarity indicates the amount of material dissolved in the water. Cloudy water might be all right if the material in it is not organic, such as sand. Clear water could be swarming with microbes.

 

- Spring Water: Ground water is usually cleaner than surface water because of filtration through soil. It may contain higher amounts of chemicals, toxic heavy metals or radioactive material.

 

My first choice is spring water from a clean source. After that, I prefer water least likely to have been bothered by humans or their animals. I avoid water frequented by dogs, cows, and pack animals, and water gathered near trails and popular camping sites.

 

METHODS OF WATER DISINFECTION

 

Microbe killing by heat or chemicals is exponential. Total killing is impractical. The goal is a 3 to 5 log reduction (99.9% to 99.999% killing).

 

Disinfection methods can be combined. The following are common methods:

 

- CHEMICAL DISINFECTION

 

The most common chemical disinfectants are the halogens chlorine and iodine. These are strong oxidants and are effective against all microorganisms. Iodine is about 40 times more potent than chlorine against virus. Mixed oxidation products (Mioxx) kill by the same process.

 

Bacteria are the most sensitive to halogens, virus are ten fold less sensitive than bacteria. Parasites and cysts are the least sensitive

 

Microbes are killed by chemical reactions with microbes. Actions that speed up or encourage more complete chemical reaction increase killing. Actions that increase killing include:

 

-Warming.

-Stirring, shaking, or agitating.

-Increasing the exposure time to chemicals.

-Increasing the concentration of chemicals.

-Filtering to remove "clumps" of sequestered microbes before adding chemicals.

-Decreasing the number of microbes by any means before chemicals are added.

 

-For cooler water , cloudy water with higher concentrations of microbes, increase the amount of halogen and/or the time of exposure .

 

-pH makes a difference: Alkaline desert water, water running through granite, or surface water made acidic by acid rain requires more halogen, longer exposure, etc. Halogen tablets might provide some pH buffering.

 

-If in question, double the dose of halogen. But remember that very strong concentrations of halogens irritate the mouth, stomach and other membranes. Some people are allergic to halogens.

 

- Prolonged use of iodine can affect the thyroid gland. Limit exposure to iodine if pregnant.

 

-Adding a reducing agent (acid) to iodine solution inactivates it by changing iodine ions to iodide. Iodide has no taste, color or smell and is less irritating

but it doesn’t kill microbes. Citric or ascorbic acid in fruit drinks or vitamin C tablets inactivate iodine.

 

- PASTEURIZATION 

 

- Disinfection by heat is called Pasteurization. Heating or boiling kills or inactivates all water borne pathogens. Higher temperatures hasten killing, but temperature above 140 F (60 C) is adequate. (This is contrary to old recommendations).

 

 

-Bringing water to a boil for one minute and allowing it to cool slowly provides a good safety margin. Altitude is not a significant factor.

 

METHODS OF PURIFICATION

 

-FILTERING

 

-Filtering clarifies water by removing "clumps" of material. The clumps might include toxic chemicals or microbes, but filtering does not kill microbes. Sequential filtering steps are helpful.

 

-Enteric bacteria are about 2/10 micrometer, protozoal cysts are 1 micrometer and larger. Check your filter’s pore size. Remember that virus are much smaller and the most important organisms.

 

-Standard filters can remove larger organisms, especially if they are "clumped". Ceramic filters might remove some clumped virus, but does not purify to recommended levels.

 

-Filtration alone might be adequate in pristine watersheds with excellent water, but is not adequate in high use areas or for foreign travel.

 

-Alum forms a gel which binds dissolved material. Adding a "pinch" of Alum to a gallon of water, and then stirring, shaking and agitating for 5 minutes before allowing it to settle for 30 minutes before filtering or decanting will help clarify water.  It imparts a strong taste to water.

 

-GRANULAR ACTIVATED CHARCOAL (GAC)

 

-Activated charcoal (GAC) works by absorbing chemicals. Charcoal is the best way to remove toxic chemicals from water and to improve the color and taste of water.

 

-Activated charcoal (GAC) does not kill microorganisms. They can remain alive in the charcoal.

 

-Activated charcoal (GAC) absorbs chlorine and iodine (use charcoal after chemical disinfection).

 

-Activated charcoal (GAC) a finite shelf life. It lasts months, or perhaps longer with infrequent use. You can test to see if it is spent by seeing how well it removes food coloring from water.

 

-IODINE RESINS

 

-Resins work by bringing water in contact with the iodine ions attached to the resin.

 

-Resins have been used in "drink through" filter bottles. Effectiveness is limited in that water spends so little time in contact with the resin that minimal killing occurs. Multiple stages of filtration and passing water through the filter several times may be helpful.

 

ESSENTIAL POINTS

 

1. Very little specific research has been done on individual treatment of water in the wilderness.

2. Infection is primarily due to human and animal waste. High use areas present the greatest risk. Infection usually causes diarrhea.

3. Good field sanitation to avoid "oral-fecal" spread is more important than water treatment.

4. Filtration clarifies water by physically removing "clumps" of organic and inorganic materials. Filtration may reduce microbe count, but is adequate only if water is not highly contaminated.

5. Iodine kills microbes, but it takes time. Ascorbic acid deactivates killing and improves the taste of iodine solutions. Warm, clear water requires less iodine.

6. Heating kills microbes. Prolonged boiling isn’t necessary.

7. GAC removes chemicals and improves the taste and smell of water but has a limited shelf life.

8. The effectiveness of "drink through" filters is doubtful.

9. Staged treatment of water might include filtration followed by boiling and/or iodine or chlorine treatment, followed by activated charcoal exposure.

10. Clear spring water obtained far from a trail or camping area is great stuff.

 

FOR DISCUSSION: What are the strengths and weakness of these methods?

 

1. Joe uses an old "drink through" filter bottle he bought at a garage sale years ago. It appears to contain a paper filter and some activated charcoal. (Old, inactive charcoal, no microbe "killing").

 

2. Alice uses a small commercial backpacking filter. She prefers to pump cold water from the bottom of fast-moving streams near trails and camp sites. (No "killing", possible high microbe contamination by human wastes. Cold water "holds" microbes longer. Sediment contains more microbes than water at the top of the stream.)

 

3. Bill puts iodine in his water to kill microbes. He then adds lemonade to get rid of the iodine taste and drinks the water immediately. (Citric acid inactivates iodine, iodine takes time to kill).

 

4. Charles brings his water to a full rolling boil for 10 minutes before he will use it. He boils the water an additional minute for each 1,000 feet of elevation. (Excessive treatment wastes fuel).

 

5. Buck doesn’t bother to treat any of his water. He says he is "used to" bad water, and he can always get treatment later if he gets sick. (You don’t build significant immunity to diarrheal diseases. There are a few diseases - mostly viral - that have no treatment).

 

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Dr. Bob Armstrong, N7XJ, is a longtime QRPer and expert outdoorsman. He's also a country doctor living in Manti, UT.

 

 

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